: Steam lines must be pitched so that water drains back to the boiler. Sounds like water is trapped in one of the lines.

: : I have a steam radiator system where the pipes make loud clanging noises whenever the heating comes on. What can I do to stop the clanging?: : Thank you for your help.

"One opinion" is on the money. Steam flows throughout the pipes above the heavier water which follows the pitch downward back to your steam boiler. Chances are the lines are pitched ok. Would be worth looking at the radiators themselves too.